When installing a prosthesis for replacing a joint within the body, a portion of a bone is generally resected and a cavity is formed for receiving a prosthesis having a portion for forming a joint. A resection may be performed using a tool with a cutting edge, such as a chisel that is forced across an end of the bone to form a flat surface on which the prosthesis can transfer loads to the bone, or to remove a portion of bone that is damaged or deficient. A cavity is formed by a tool with a cutting edge driven longitudinally into the bone, such as a chisel, reamer or rasp. The cavity extends down the medulary canal and receives the stem of the prosthesis, which is used to provide some stability for the joint. In the implantation of a hip joint prosthesis, the head at the proximal end of the femur is removed and a hole is formed in the medullary canal of the femur. The cavity is then shaped so as to conform to the shape of the prosthesis selected by the surgeon according to the patient's indications.
Tools for shaping a cavity in a bone are known. A support having a guide arm for guiding a reamer in shaping a cavity in the femur is known. This apparatus requires a number of parts, including at least one guide arm which must be connected to an upper end of the guide body. A guide arm for the anterior side, as well as another guide arm for the posterior side must be attached to the upper end of the guide body, in order to shape both the anterior and posterior sides of the cavity. This apparatus complicates the method for shaping the cavity in the femur and includes many parts. Further, the guide arm allows the reamer to deviate from the path that produces the desired shape for the cavity. Another support has a guide bar that guides pivoting of a reamer. This system requires a plurality of supports and a multitude of reamers that correspond to different sized prostheses. Thus, the inventory of instruments is large and complicates preparation for, as well as the conduct of, the surgical procedure.
A plurality of different guide arms which can be selected according to the size of the prosthesis to be installed has also been proposed. However, this apparatus suffers from the drawbacks mentioned above.
A guide for shaping a cavity within an end of a bone for receiving a prosthesis, which simplifies the method of shaping the bone, is desirable. In addition, an apparatus that is adaptable according to the size of the prosthesis to be installed is also desired.